Shareholders' Equity - Summary of common shareholders' equity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 25,442	$ 20,880
Net income	1,753	4,597
Retirement benefits adjustment	(17)	11
Compensation expense	100	101
Purchase of treasury shares	(275)	(114)
Cash dividend	(380)	(375)
Exercise of stock options, net of tax benefit		4
Stock based compensation, net of tax benefit	494	338
Balance	$ 27,117	$ 25,442
Balance (shares)	2,614,506	2,614,506
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 523	$ 523
Balance (shares)	2,614,506	2,614,506
Net income
Retirement benefits adjustment
Compensation expense
Purchase of treasury shares
Cash dividend
Exercise of stock options, net of tax benefit
Stock based compensation, net of tax benefit
Balance	$ 523	$ 523
Balance (shares)	2,614,506	2,614,506
Capital in excess of par value
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	$ 14,092	$ 14,068
Net income
Retirement benefits adjustment
Compensation expense
Purchase of treasury shares
Cash dividend
Exercise of stock options, net of tax benefit
Stock based compensation, net of tax benefit	68	24
Balance	14,160	14,092
Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	13,395	9,176
Net income	1,753	4,597
Retirement benefits adjustment
Compensation expense
Purchase of treasury shares
Cash dividend	(380)	(375)
Exercise of stock options, net of tax benefit		(3)
Stock based compensation, net of tax benefit
Balance	14,768	13,395
ESOT
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(863)	(964)
Net income
Retirement benefits adjustment
Compensation expense	100	101
Purchase of treasury shares
Cash dividend
Exercise of stock options, net of tax benefit
Stock based compensation, net of tax benefit
Balance	(763)	(863)
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(1,702)	(1,909)
Net income
Retirement benefits adjustment
Compensation expense
Purchase of treasury shares	(275)	(114)
Cash dividend
Exercise of stock options, net of tax benefit		7
Stock based compensation, net of tax benefit	426	314
Balance	(1,551)	(1,702)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	(3)	(14)
Net income
Retirement benefits adjustment	(17)	11
Compensation expense
Purchase of treasury shares
Cash dividend
Exercise of stock options, net of tax benefit
Stock based compensation, net of tax benefit
Balance	$ (20)	$ (3)